Device for holding and contacting thermally loaded ceramic resistors in a case

ABSTRACT

The invention relates to a device for holding and contacting thermally loaded ceramic resistors. Thermally loaded ceramic resistors such as PTC resistors are generally brittle and, while they have the characteristic of a substantial temperature expansion coefficient, they are relatively weak structurally. The device hereof which accommodates a PTC resistor includes resiliently biased electrical contacts which old the resistor firmly in a fixed position while permitting the resistor to expand freely upon being heated without incurring stresses wihch would cause breakage.

United States Patent [191 on 3,842,188

Petersen Oct. 15, 1974 541 DEVICE FOR HOLDING AND CONTACTING 3,130,032 7/1373 Petersen at al. 333/333 x THERMALLY LOADED CERAMIC RESISTORS IN A CASE Poul Petersen, Nordborg, Denmark Assignee: Danfoss A/S, Nordborg, Denmark Filed: Nov. 12, 1973 Appl. No.: 415,119

Inventor:

Foreign Application Priority Data Nov. 14, I972 Germany 2255664 US. Cl. 174/52 R, 338/57, 338/220, 338/232, 338/316 Int. Cl H016 1/02, HOlc 1/08 Field of Search 174/16 R, 52 R; 338/22 R, 338/53, 57, 220, 226, 232, 315, 316

References Cited UNITED STATES PATENTS 7/1973 Halstead l74/52 R Primary Examiner -Laramie E. Askin [57] ABSTRACT The invention relates to a device for holding and contacting thermally loaded ceramic resistors. Thermally loaded ceramic resistors such as PTC resistors are generally brittle and, while they have the characteristic of a substantial temperature expansion coefficient, they are relatively weak structurally. The device hereof which accommodates a PTC resistor includes resiliently biased electrical contacts which old the resistor firmly in a fixed position while permitting the resistor to expand freely upon being heated without incurring stresses wihch would cause breakage.

1 Claim, 5 Drawing Figures PATENIEUUCT 1 51914 SHEET 20F 2 3 SHQ Q DEVICE FOR HOLDING AND CONTACTING THERMALLY LOADED CERAMIC RESISTORS IN A CASE Devices are known for holding and contacting thermally loaded ceramic resistors in a case, in particular PTC resistors, in which device the resistor body is held in position by electrical contacts which bear in a mechanically positive manner agains the planar end faces of the body. It is also known to loosely guide the resistor body at its median portion in a hole which corresponds to the cross section of the body and is formed in a disc made of electrically insulating heat resisting material and held in the case. In this arrangement, the case may consist of two interconnected parts. This enables the ceramic resistor to be held and contacted very firmly without the danger of the resistor being irreparably damaged. Furthermore, the surface of the resistor body can be reached by the surrounding air over a large area, so that uniform heating and cooling of the surface results.

The object of the present invention is that of further simplifying the construction of such device.

This object is achieved by making the disc in two parts which are formed by ribs integrally injection moulded with the two parts of the case.

In this construction it is not necessary to produce the disc as a separate component. Holding means for securing the disc in the case are also unnecessary. A very simple construction therefore results.

Particular advantage is achieved if that part of the case that carries the'electrical contacts applied in a mechanically positive manner has a rib which surrounds the resistor body over approximately 180. The resistor body can therefore be mounted practically entirely in one of the parts of the case. The rib provided on the second part of the case is then only required to ensure that the resistor body cannot at a later stage move out of the assembly position so achieved.

In a preferred embodiment the rib which surrounds the resistor body is provided with parallel extensions and is connected through transverse webs only at the ends of these extensions and at the middle of the rib. In this way very large ventilation openings are created between the side walls of the casing, which openings are covered only by the width of the rib.

It suffices if the rib on the other part of the case is associated with a peripheral portion of the resistor body that occupies considerably less than 180 of the circumference of said body. In the extreme case it suffices if said rib is associated with a point on this peripheral portion.

The invention will now be described in greater detail by reference to a form of construction illustrated in the drawing, in which:

FIG. 1 is a longitudinal section through a resistor holding device in accordance with the invention,

FIG. 2 is a cross section on line 2-2 of FIG. 1;

FIG. 3 is a vertical elevation view of the right side of the view shown in FIG. 1;

FIG. 4 is a vertical elevational view with parts broken away of the left side of the view shown in FIG. 1; and

FIG. 5 is a top view partially in section of the view shown in FIG. 1.

The device has a case consisting of two parts 1 and 2 which are brought into register with each other by means of an edge 3 and are interconnected by a rivet 4. A PTC resistor body 5 in the form of a cylindrical disc is held loosely by its median part in a hole 6 which is formed in a disc constituted by two ribs 7 and 8. The rib 7 is integrally injection moulded with part I of the case, and the rib 8 with part 2 of the case. Double contacts 9 and 10 engage the two end faces of the resistor body 5. These contacts are parts of contact plate sections 11 which bear against the side walls 12 and 13 of part 1 of the case and project outwardly to form terminal connections 14.

In the present embodiment, the hole 6 formed by the ribs 7 and 8, receiving the disc, is not round. Instead, only a l-portion of the rib 7 is associated with the periphery of the resistor body 5, and the rib 8 is associated with a bearing point. However this suffices to hold the resistor body 5 in position between the resilient contacts 9 and 10.

The rib 7 has two extensions 15 and 16. It is connected to the side walls 12 and 13 by transverse webs l7, l8 and 19 only at the ends of these extensions and at the middle of the rib. Consequently, large ventilation openings 20 and 21, through which air for cooling the resistor body 5 may pass, are left at both sides of the rib 7 and of its extensions 15 and 16.

When assembling the device, the resistor body 5 together with the contact plates 11 are pushed into part 1 of the case. As this happens, the rib 7 holds the resistor body in its final position. Application of the rib 8 when part 2 of the case is fitted ensures that this position is also maintained during operation.

The material of the entire case may be any one of a large number of electrically insulating heat resisting plastic substances.

I claim:

1. A device for holding and contacting a thermally loaded disc shaped ceramic resistor comprising a casing having first and second parts, means fastening said parts together, said first casing part having a U-shaped rib straddled by U-shaped end walls, web means connecting said end walls and said U-shaped rib, said second casing part having a rectangularly shaped rib aligned with said U-shaped rib to form a resistor cavity therebetween, and a pair of resilient electrical contacts disposed on opposite sides of said cavity for resiliently engaging the opposite sides of a resistor when disposed in said cavity and for resiliently engaging said end walls. a: =k 

1. A device for holding and contacting a thermally loaded disc shaped ceramic resistor comprising a casing having first and second parts, means fastening said parts together, said first casing part having a U-shaped rib straddled by U-shaped end walls, web means connecting said end walls and said U-shaped rib, said second casing part having a rectangularly shaped rib aligned with said U-shaped rib to form a resistor cavity therebetween, and a pair of resilient electrical contacts disposed on opposite sides of said cavity for resiliently engaging the opposite sides of a resistor when disposed in said cavity and for resiliently engaging said end walls. 